Recently, further eagerer study than before has been made for high-densification of an optical disk. In the case where recording conditions such as a recording light quantity of a light beam projected to an optical disk or a recording magnetic field strength of an external magnetic field applied to a magneto-optical recording disk vary, a size of a record mark accordingly varies, thereby causing uniform recording to be failed, and as a result high-density recording is hardly possible.
Therefore, the Japanese Publication for Laid-Open Patent Application No. 16965/1997 (Tokukaihei 9-16965), for example, discloses a device for optimizing a recording light quantity of a light beam at an ON time by doing the following controlling operation, which device is for use in a so-called light modulation recording apparatus wherein data is recorded by ON/OFF of the light beam.
First, the recording light quantity is gradually increased, while record marks are recorded at each time. Then, each record mark becomes longer as the recording light quantity increases, and a so-called duty, which is a ratio of the record marks to portions other than the record mark, varies. The variation of the duty is easily recognized by detecting a DC component of a reproduction signal. Therefore, a recording light quantity which corresponds to such a record mark that the duty becomes 1:1 is found among the record marks recorded with a recording light quantity which gradually alters, and the light quantity thus found is selected an optimal light quantity. By doing so, the record marks always have optimal lengths. The foregoing device performs such recording light quantity control.
Such a light modulation recording apparatus, however, has the following drawback. A change in the size of the record mark in a lengthwise direction (a direction along a track) appears in the duty, whereas a change in the size of the record mark in a width direction (a direction orthogonal to the track) which is orthogonal to the lengthwise direction does not appear therein. Therefore, the width of the record mark cannot be optimized.
More specifically, with the conventional apparatus, narrow record marks 101 are recorded by a light beam 105 with a small recording light quantity, as shown in FIG. 18(a). On the other hand, as shown in FIG. 18(b), wider record marks 102 than the record marks 101 are recorded by a light beam 106 with a greater recording light quantity. However, such variation of the width of the record marks does not appear in respective duties of recording signals 103 and 104. For this reason, conventionally, controlling the width of the record marks to an appropriate value was impossible. As a result, the width of the record marks varied, and crosstalk upon reproduction of a signal which occurred as high-densification of recording tracks was furthered, or crosserase upon recording of a signal (erasure of ends of record marks due to effusion of record from an adjacent track), could not be minimized, thereby making it impossible to arrange tracks at a higher density.
On the other hand, instead of the light modulation recording, a so-called magnetic field modulation recording whereby data are recorded by reversing an external magnetic field may be executed in a recording operation with respect to a magneto-optical disk. In this case, the recording light quantity is constant, not being turned ON/OFF.
As for the magnetic field modulating recording, narrow record marks 101 are recorded, as shown in FIG. 18(a), in the case where a recording light quantity of a light beam is small or a strength of a recording magnetic field is small. On the other hand, as shown in FIG. 18(b), wide record marks 102 are recorded in the case where the recording light quantity of the light beam is great or the strength of the recording magnetic field is great. Here, the lengths of the record marks 101 and 102 are determined in accordance with a reversing position of the recording magnetic field, and do not depend on the recording light quantity or the recording magnetic field strength. Therefore, by appropriately controlling the reversion of the external magnetic field, record marks with appropriate lengths are precisely recorded. In this aspect, the magnetic field modulation recording differs from the light modulation recording.
However, in the case of the magnetic field modulation recording as well, a change in the width of the record marks does not appear in the duty at all. Therefore, any change in the record mark width could be detected, and hence, to control the width of the record marks was impossible.